U.S. patent application number 12/876833 was filed with the patent office on 2011-03-10 for antistatic gallium nitride based light emitting device and method for fabricating the same.
This patent application is currently assigned to XIAMEN SANAN OPTOELECTRONICS TECHNOLOGY CO., LTD.. Invention is credited to Xuejiao LIN, Qunfeng PAN, Jyh Chiarng WU.
Application Number | 20110057199 12/876833 |
Document ID | / |
Family ID | 41710456 |
Filed Date | 2011-03-10 |
United States Patent
Application |
20110057199 |
Kind Code |
A1 |
PAN; Qunfeng ; et
al. |
March 10, 2011 |
Antistatic Gallium Nitride Based Light Emitting Device and Method
for Fabricating the Same
Abstract
The invention provides an antistatic gallium nitride based light
emitting device and a method for fabricating the same. The method
includes: growing an n-type GaN-based epitaxial layer, an active
layer, a p-type GaN-based epitaxial layer and an undoped GaN-based
epitaxial layer sequentially on a substrate; etching to remove
parts of the layers above, to expose a part of the n-type GaN-based
epitaxial layer, with the unetched part defined as an emitting
area; etching to remove a part of the undoped GaN-based epitaxial
layer; forming an ohmic contact electrode on an exposed part of
p-type GaN-based epitaxial layer, and forming a Schottky contact
electrode on another part; forming a p-electrode on a transparent
conducting layer such that the p-electrode is electrically
connected with the ohmic contact electrode; forming an n-electrode
on the exposed n-type GaN-based epitaxial layer; and forming a
connecting conductor on an insulation layer such that the
connecting conductor is electrically connected with the n-electrode
and the Schottky contact electrode. By forming a GaN Schottky diode
directly on a p-type GaN-based epitaxial layer, the fabrication
process is simplified while providing antistatic ability at the
same time, and the emitting area is made the maximum use of so as
to avoid the drop in the luminous efficiency of the GaN-based
LED.
Inventors: |
PAN; Qunfeng; (Xiamen City,
CN) ; LIN; Xuejiao; (Xiamen City, CN) ; WU;
Jyh Chiarng; (Xiamen City, CN) |
Assignee: |
XIAMEN SANAN OPTOELECTRONICS
TECHNOLOGY CO., LTD.
Xiamen City
CN
|
Family ID: |
41710456 |
Appl. No.: |
12/876833 |
Filed: |
September 7, 2010 |
Current U.S.
Class: |
257/76 ;
257/E21.158; 257/E33.025; 438/46 |
Current CPC
Class: |
H01L 27/15 20130101;
H01L 33/382 20130101 |
Class at
Publication: |
257/76 ; 438/46;
257/E33.025; 257/E21.158 |
International
Class: |
H01L 33/30 20100101
H01L033/30; H01L 21/28 20060101 H01L021/28 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 8, 2009 |
CN |
200910018293.5 |
Claims
1. An antistatic Gallium Nitride, GaN, based light emitting device,
comprising: a substrate; an n-type GaN-based epitaxial layer formed
on the substrate, an active layer formed on the n-type GaN-based
epitaxial layer, and a p-type GaN-based epitaxial layer formed on
the active layer; a GaN Schottky diode on a part of the p-type
GaN-based epitaxial layer, the GaN Schottky diode comprising an
undoped GaN-based epitaxial layer on said part of the p-type
GaN-based epitaxial layer, an ohmic contact electrode on a part of
the undoped GaN-based epitaxial layer and a Schottky contact
electrode on another part of the undoped GaN-based epitaxial layer;
a transparent conducting layer on another part of the p-type
GaN-based epitaxial layer; an n-electrode on a part of the n-type
GaN-based epitaxial layer; a p-electrode on the transparent
conducting layer and electrically connected with the ohmic contact
electrode; an insulation layer formed on side surfaces of the
undoped GaN-based epitaxial layer, the p-type GaN-based epitaxial
layer, the active layer and the n-type GaN-based epitaxial layer;
and a connecting conductor on the insulation layer and another part
of the n-type GaN-based epitaxial layer, and electrically connected
with the Schottky contact electrode and the n-electrode.
2. The antistatic GaN-based light emitting device according to
claim 1, wherein: the ohmic contact electrode is made of Ti, or Al,
or Cr, or any combination thereof.
3. The antistatic GaN-based light emitting device according to
claim 1, wherein: the Schottky contact electrode is made of Pt, or
Au, or Ni, or any combination thereof.
4. The antistatic GaN-based light emitting device according to
claim 1, wherein: the insulation layer is made of silicon dioxide,
silicon nitride, titanium oxide, aluminum oxide or polyimide.
5. The antistatic GaN-based light emitting device according to
claim 1, wherein: the connecting conductor is made of metal, metal
alloy, metal oxide, or semiconductor having good conductivity, or
any combination thereof.
6. A method for fabricating an antistatic Gallium Nitride, GaN,
based light emitting device, comprising: 1) growing an n-type
GaN-based epitaxial layer, an active layer, a p-type GaN-based
epitaxial layer and an undoped GaN-based epitaxial layer on a
substrate sequentially; 2) etching to remove parts of the undoped
GaN-based epitaxial layer, the p-type GaN-based epitaxial layer,
the active layer and the n-type GaN-based epitaxial layer, to
expose a part of the n-type GaN-based epitaxial layer, with the
unetched part defined as an emitting area; 3) etching to remove the
undoped GaN-based epitaxial layer on a part of the emitting area,
to expose a part of the p-type GaN-based epitaxial layer; 4)
forming an ohmic contact electrode on a part of the undoped
GaN-based epitaxial layer, and forming a Schottky contact electrode
on another part of the undoped GaN-based epitaxial layer; 5)
forming a transparent conducting layer on the exposed p-type
GaN-based epitaxial layer; 6) forming a p-electrode on the
transparent conducting layer such that the p-electrode is
electrically connected with the ohmic contact electrode; 7) forming
an n-electrode on the exposed n-type GaN-based epitaxial layer; 8)
forming an insulation layer on a sidewall surface of the emitting
area; and 9) forming a connecting conductor on the insulation layer
such that the connecting conductor is electrically connected with
the n-electrode and the Schottky contact electrode.
7. The method for fabricating an antistatic GaN-based light
emitting device according to claim 6, wherein: in step 3) the
undoped GaN-based epitaxial layer is etched using wet chemical
etching.
Description
[0001] This application claims the benefit of Chinese patent
application No. 200910018293.5 titled "Antistatic Gallium Nitride
based Light Emitting Device and Method for Fabricating the Same",
and filed with the Chinese Patent Office on Sep. 8, 2009, which is
hereby incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a gallium nitride based
light emitting device and a method for fabricating the same, and in
particular to an antistatic gallium nitride based light emitting
device and a method for fabricating the same.
BACKGROUND OF THE INVENTION
[0003] As a revolutionary invention in the field of lighting in the
21.sup.st century, semiconductor lighting has gained a lot of
attention from governments, scholars and related institutions
worldwide. As for its current development, Gallium Nitride (GaN)
based Light Emitting Diodes (LEDs) are the basis for realizing
semiconductor lighting. As the technologies of epitaxial growth and
chip process advance, internal quantum efficiency and extraction
efficiency of GaN-based LEDs have been greatly improved, and
luminous efficiency of lighting-class whites is now up to 161 lm/W.
Although the luminous efficiency is relatively high, damages to the
GaN-based LEDs due to electrostatics are still a serious problem in
the application of the GaN-based LEDs. Currently, a common approach
to protect a GaN-based LED from electrostatic damages is to connect
it in parallel with a Zener diode during encapsulation; however,
this would increase encapsulation complexity and manufacture costs.
Consequently, a more advantageous approach is to integrate the
GaN-based LED structure with an electrostatic protection diode
structure in a light emitting device, so that the whole light
emitting device is antistatic.
[0004] The document "S-J Chang, C-H Chen, Y-K Su, et al., Improved
ESD Protection by combining InGaN-GaN MQW LEDs with GaN Schottky
diodes, IEEE Electron Device Letters, Vol. 24, No. 3, pp 129-131,
2003" proposed a GaN-based light emitting device integrated with a
Schottky diode. FIG. 1a illustrates a sectional view of its
structure, and FIG. 1b illustrates an equivalent circuit. With
reference to FIG. 1a, the light emitting device includes a
GaN-based LED and a GaN Schottky diode. The GaN-based LED structure
includes: a sapphire substrate 101; a buffer layer 102, a u-GaN
layer 120, an n-GaN layer 103, a multi-quantum well active layer
104, a p-AlGaN barrier layer 105, a p-GaN layer 106 and a
transparent conducting layer 111 formed in that order on the
sapphire substrate 101; a p-electrode 112 on the transparent
conducting layer 111; and, an n-electrode 113 on the exposed n-GaN
layer 103. The GaN Schottky diode is formed in the GaN-based LED
structure and is electrically isolated by a SiO.sub.2 insulation
layer 123 from the GaN-based LED structure except the transparent
conducting layer 111, the p-electrode 112 and the n-electrode 113.
The GaN Schottky diode structure includes: the sapphire substrate
101, the buffer layer 102 on the sapphire substrate 101, the u-GaN
layer 120 on the buffer layer 102, an ohmic contact electrode 121
on a part of the u-GaN layer 120, and a Schottky contact electrode
122 on another part of the u-GaN layer 120. The ohmic contact
electrode 121 is electrically connected with the p-electrode 112,
and the Schottky contact electrode 122 is electrically connected
with the n electrode 113. Therefore, the light emitting device is
equivalently the GaN-based LED connected in parallel with the GaN
Schottky diode, and the equivalent circuit is shown in FIG. 1b. As
for the GaN-based LED, when a forward voltage is applied, almost
all the current flows through the LED; and when an instantaneous
backward electrostatic voltage is applied, it could be discharged
through the GaN Schottky diode, i.e., most of the current flows
through the Schottky diode, thereby reducing the damage to the
GaN-based LED.
[0005] However, as the Schottky diode is formed in the LED
structure, the conventional antistatic GaN-based light emitting
device described above is of great fabrication difficulty and
accuracy, and therefore is not suitable for mass production. In
order to form the "built-in" Schottky diode, the epitaxial
structure has to be etched to the u-GaN layer, which requires a
thickened u-GaN layer (otherwise the processing window for etching
may be too narrow); however, a thickened u-GaN layer means a cost
increase. On the other hand, the presence of the "built-in"
Schottky diode takes emitting areas, hence increasing current
density of the active area and degrading the luminous efficiency.
The case would be even worse while the size of the chip is
small.
SUMMARY OF THE INVENTION
[0006] In order to solve the problems above, the present invention
is to provide an antistatic GaN-based light emitting device and a
method for fabricating the same. By forming a GaN Schottky diode
directly on a p-type GaN-based epitaxial layer, the fabrication
process is simplified while providing antistatic ability at the
same time, and the emitting area is made the maximum use of so as
to avoid the drop in the luminous efficiency of the GaN-based
LED.
[0007] To achieve the object above, the present invention provides
an antistatic GaN-based light emitting device, the structure of
which including:
[0008] a substrate;
[0009] an n-type GaN-based epitaxial layer on the substrate, an
active layer on the n-type GaN-based epitaxial layer, and a p-type
GaN-based epitaxial layer on the active layer;
[0010] a GaN Schottky diode on a part of the p-type GaN-based
epitaxial layer, the GaN Schottky diode including an undoped
GaN-based epitaxial layer on said part of the p-type GaN-based
epitaxial layer, an ohmic contact electrode on a part of the
undoped GaN-based epitaxial layer and a Schottky contact electrode
on another part of the undoped GaN-based epitaxial layer;
[0011] a transparent conducting layer on another part of the p-type
GaN-based epitaxial layer;
[0012] an n-electrode on a part of the n-type GaN-based epitaxial
layer;
[0013] a p-electrode on the transparent conducting layer and
electrically connected with the ohmic contact electrode;
[0014] an insulation layer formed on side surfaces of the undoped
GaN-based epitaxial layer, the p-type GaN-based epitaxial layer,
the active layer and the n-type GaN-based epitaxial layer; and
[0015] a connecting conductor on the insulation layer and another
part of the n-type GaN-based epitaxial layer, and electrically
connected with the Schottky contact electrode and the
n-electrode.
[0016] A novel part of the device according to the present
invention is that the GaN-based LED is integrated with the GaN
Schottky diode in the same light emitting device, and the GaN
Schottky diode is formed on a part of the p-type GaN-based
epitaxial layer of the GaN-based LED; the GaN-based LED and the GaN
Schottky diode are electrically connected in parallel with their
polarities reversed, particularly, the ohmic contact electrode is
electrically connected with the p-electrode, and the Schottky
contact electrode is electrically connected with the n-electrode
via the connecting conductor; and in order to avoid short circuits
caused by the connecting conductor between the sidewalls of the
epitaxial layers, the insulation layer is formed between the
connecting conductor and the sidewall surfaces of the epitaxial
layers for electrical isolation.
[0017] In the device according to the invention, the ohmic contact
electrode is made of Ti, Al, or Cr, or any combination thereof; the
Schottky contact electrode is made of Pt, Au, or Ni, or any
combination thereof; the insulation layer is made of silicon
dioxide, silicon nitride, titanium oxide, aluminum oxide or
polyimide; and the connecting conductor is made of metal, metal
alloy, metal oxide or semiconductor having good conductivity, or
any combination thereof.
[0018] The present invention also provides a method for fabricating
the antistatic GaN-based light emitting device above, including the
steps of:
[0019] 1) growing an n-type GaN-based epitaxial layer, an active
layer, a p-type GaN-based epitaxial layer and an undoped GaN-based
epitaxial layer on a substrate sequentially;
[0020] 2) etching to remove parts of the undoped GaN-based
epitaxial layer, the p-type GaN-based epitaxial layer, the active
layer and the n-type GaN-based epitaxial layer, to expose a part of
the n-type GaN-based epitaxial layer, with the unetched part
defined as an emitting area;
[0021] 3) etching to remove the undoped GaN-based epitaxial layer
on a part of the emitting area, to expose a part of the p-type
GaN-based epitaxial layer;
[0022] 4) forming an ohmic contact electrode on a part of the
undoped GaN-based epitaxial layer, and forming a Schottky contact
electrode on another part of the undoped GaN-based epitaxial
layer;
[0023] 5) forming a transparent conducting layer on the exposed
p-type GaN-based epitaxial layer;
[0024] 6) forming a p-electrode on the transparent conducting layer
such that the p-electrode is electrically connected with the ohmic
contact electrode;
[0025] 7) forming an n-electrode on the exposed n-type GaN-based
epitaxial layer;
[0026] 8) forming an insulation layer on a sidewall surface of the
emitting area; and
[0027] 9) forming a connecting conductor on the insulation layer
such that the connecting conductor is electrically connected with
the n-electrode and the Schottky contact electrode.
[0028] In the method above according to the present invention, in
step 3) the undoped GaN-based epitaxial layer is etched using wet
chemical etching; and in order to form the GaN Schottky diode on
the p-type GaN-based epitaxial layer, the undoped GaN-based
epitaxial layer is added with the present invention to the
conventional epitaxial structure. In patterning of the undoped
GaN-based epitaxial layer, selective etching of the undoped
GaN-based epitaxial layer over the p-type GaN-based epitaxial layer
is a serious issue. With dry etching, damages to the p-type
GaN-based epitaxial layer would be hard to avoid and the contact
resistance with the transparent conducting layer would be
increased; therefore, the invention uses wet chemical etching to
etch the undoped GaN-based epitaxial layer. In certain conditions,
the p-type GaN-based epitaxial layer cannot be etched with wet
chemical etching. Therefore, its surface characteristics can be
well maintained, which is good for forming a good ohmic contact
with the transparent conducting layer.
[0029] Advantageous effects brought by the present invention
include: by forming a GaN Schottky diode directly on a p-type
GaN-based epitaxial layer, the fabrication process is simplified
while providing antistatic ability at the same time; manufacture
costs are lowered; and the emitting area is made the maximum use of
so as to avoid the drop in the luminous efficiency of the GaN-based
LED, thereby solving the problem in the prior art that the
conventional antistatic GaN-based light emitting device is complex
in its fabrication process and has a degraded luminous
efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1a is a sectional view of an existing antistatic
GaN-based light emitting device;
[0031] FIG. 1b illustrates an equivalent circuit of the existing
antistatic GaN-based light emitting device;
[0032] FIG. 2 is a sectional view of an antistatic GaN-based light
emitting device according to an embodiment of the invention;
and
[0033] FIG. 3a to FIG. 3d are sectional views illustrating a
fabrication process of an antistatic GaN-based light emitting
device according the invention.
[0034] Components in the drawings include: [0035] 101 Substrate
[0036] 102 Buffer layer [0037] 103 n-GaN layer [0038] 104
Multi-quantum well active layer [0039] 105 p-AlGaN barrier layer
[0040] 106 p-GaN layer [0041] 111 transparent conducting layer
[0042] 112 p-electrode [0043] 113 n-electrode [0044] 120 u-GaN
layer [0045] 121 ohmic contact electrode [0046] 122 Schottky
contact electrode [0047] 123 SiO.sub.2 insulation layer [0048] 124
connecting conductor
DETAILED DESCRIPTION OF THE INVENTION
[0049] The invention is further described hereinafter in connection
with FIG. 2 and FIG. 3a to FIG. 3d and the preferred
embodiments.
[0050] As shown in FIG. 2, a sectional view of an antistatic
GaN-based light emitting device according to a preferred embodiment
of the invention, it includes: a sapphire substrate 101, a buffer
layer 102, an n-GaN layer 103, a multi-quantum well active layer
104, a p-AlGaN barrier layer 105, a p-GaN layer 106, an ITO
transparent conducting layer 111, a p-electrode 112, an n-electrode
113, a u-GaN layer 120, an ohmic contact electrode 121, a Schottky
contact electrode 122, an SiO.sub.2 insulation layer 123 and a
connecting conductor 124.
[0051] Particularly, the sapphire substrate 101, the buffer layer
102, the n-GaN layer 103, the multi-quantum well active layer 104,
the p-AlGaN barrier layer 105, the p-GaN layer 106, the ITO
transparent conducting layer 111, the p-electrode 112 and the
n-electrode 113 form a GaN-based LED; and, the u-GaN layer 120, the
ohmic contact electrode 121 and the Schottky contact electrode 122
form a GaN Schottky diode.
[0052] The structure of the GaN-based LED includes: the sapphire
substrate 101 at the bottom; the buffer layer 102 formed on the
sapphire substrate 101; the n-GaN layer 103 formed on the buffer
layer 102; the multi-quantum well active layer 104 formed on the
n-GaN layer 103; the p-AlGaN barrier layer 105 formed on the
multi-quantum well active layer 104; the p-GaN layer 106 formed on
the p-AlGaN barrier layer 105; the transparent conducting layer 111
formed on a part of the p-GaN layer 106 and made of Indium Tin
Oxide (ITO); the p-electrode 112 formed on the transparent
conducting layer 111 and made of Cr/Pt/Au; and, the n-electrode 113
formed on a part of the n-GaN layer 103 and made of Cr/Pt/Au.
[0053] The GaN Schottky diode is formed on a part of the p-GaN
layer 106, and the structure of the GaN Schottky diode includes:
the u-GaN layer 120 formed on a part of the p-GaN layer 106; the
ohmic contact electrode 121 formed on a part of the u-GaN layer 120
and made of Ti/Al alloy; and, the Schottky contact electrode 122
formed on another part of the u-GaN layer 120 and made of
Pt/Au.
[0054] The GaN-based light emitting device further includes the
insulation layer 123 formed on the sidewall surface of the emitting
area and made of SiO.sub.2; and, the connecting conductor 124
formed on the insulation layer 123 and the n-GaN layer 103 and made
of Pt/Au.
[0055] Particularly, the p-electrode 112 is electrically connected
with the ohmic contact electrode 121, and the n-electrode 113 and
the Schottky contact electrode 122 are electrically connected via
the connecting conductor 123.
[0056] A method for fabricating the antistatic GaN-based light
emitting device according to the preferred embodiment shown in FIG.
2 is described below:
[0057] As shown in FIG. 3a, with the sapphire substrate 101 being
the substrate, the buffer layer 102, the n-GaN layer 103, the
multi-quantum well active layer 104, the p-AlGaN barrier layer 105,
the p-GaN layer 106 and the u-GaN layer 120 are grown on the
sapphire substrate 101 sequentially using a Metalorganic chemical
vapor deposition (MOCVD) method, to form a GaN-based LED epitaxial
wafer.
[0058] As shown in FIG. 3b, by using a photoresist as a mask and to
define an emitting area, the u-GaN layer 120, the p-GaN layer 106,
the p-AlGaN barrier layer 105 and the multi-quantum well active
layer 104 outside the emitting area are removed using Inductively
Coupled Plasma (ICP) dry etching, to expose the n-GaN layer 103.
And by using a photoresist as a mask and to define the Schottky
diode region, the u-GaN layer 120 on the emitting area except the
Schottky diode region is removed using wet chemical etching, to
expose the p-GaN layer 106. For maximum use of the emitting area,
the Schottky diode region may be defined as surrounding the
emitting area.
[0059] As shown in FIG. 3c, Ti/Al alloy is deposited on a part of
the u-GaN layer 120 by evaporation, to form the ohmic contact
electrode 121; Pt/Au is deposited on another part of the u-GaN
layer 120 by evaporation, to form the Schottky contact electrode
122; the SiO.sub.2 insulation layer 123 is deposited on the
sidewall surface of the emitting area using a Chemical Vapor
Deposition (CVD) method, the SiO.sub.2 insulation layer 123
covering all or a part of the side surface of the emitting area;
and, Pt/Au is deposited on the SiO.sub.2 insulation layer 123 by
evaporation as the connecting conductor 124, such that the
connecting conductor 124 forms a good electrical connection with
the Schottky contact electrode 122.
[0060] As shown in FIG. 3d, the ITO transparent conducting layer
111 is deposited on the p-GaN layer 106 by evaporation; Cr/Pt/Au is
deposited on the ITO transparent conducting layer 111 by
evaporation, to form the p-electrode 112 such that the p-electrode
112 is in a good electrical connection with the ohmic contact
electrode 121; and, Cr/Pt/Au is deposited on the n-GaN layer 103 by
evaporation, to form the n-electrode 113 such that the n-electrode
113 is in a good electrical connection with the connecting
conductor 124.
[0061] As for electrostatic protection, the embodiments of the
invention and the conventional antistatic GaN-based light emitting
device shown in FIG. 1a both can protect the GaN-based LED from
damages. However, as compared with the prior art, the structure of
the embodiments of the invention is simpler and easier to make, and
makes maximum use of the emitting area, maintaining the original
luminous efficiency of the LED.
* * * * *